A 5-year-old boy was in critical condition after plunging from a fifth-floor window at a Bronx apartment building Tuesday night.

The youngster fell from a building on Bristow Street near Boston Road in Foxhurst at about 7:35 p.m., according to police.

“I heard the noise first. I hear the screaming and then, ‘Boom!’ ” neighbor Thomas Santiago said. “I just saw them bring the kid out on the stretcher.”

Another neighbor said the distraught mother cried out for help.

“It looked like she was about to pass out,” Migdalia Baeze said. “She was crying, hysterical.”

The boy was being treated at Lincoln Hospital Tuesday night.